In order to perform registration of a magnetic tracking system with an image of a subject, in prior art systems a probe that is tracked by the magnetic tracking system is positioned at pre-determined features of the subject. The feature locations of the probe as determined by the tracking system are correlated with the feature locations determined from an image of the subject, typically a computerized tomography (CT) image, and the correlation is used to register the image with the tracking system. However, the positioning of the probe at the pre-determined features is typically not exact, and may differ by more than 1 mm from the correct position. For example, at a given feature the probe may be pushed against the subject, depressing the skin at that location, leading to an inaccurate registration. Alternatively, at another location, the probe may not even contact the feature, again leading to an inaccurate registration.
PCT application WO2002/000093A2, to Yagel, whose disclosure is incorporated herein by reference, describes a system for registration of target object images to stored image data. Two-dimensional images are registered with both a reference coordinate system and with a previously acquired three-dimensional image of the target to provide a coordinate transformation from the reference coordinate system to the target.
US Patent application 2007/0276234, to Shahidi, whose disclosure is incorporated herein by reference, describes a method which is claimed to assist a user in guiding a medical instrument to a subsurface target site in a patient. The method is stated to generate at least one intraoperative ultrasonic image and to indicate a target site on the ultrasonic image(s).
U.S. Pat. No. 8,636,519 to Schwartz, et al., whose disclosure is incorporated herein by reference, describes a mockup probe, having a distal end and a proximal end adapted to be held by a human operator. A mockup patient, simulating an actual patient, has an aperture allowing penetration of the distal end of the mockup probe into the mockup patient. A force generator, is coupled to the mockup probe so as to apply a force to the proximal end that can be felt by the human operator, and a controller is configured to track the distal end.
U.S. Pat. No. 7,072,707 to Galloway, Jr., et al., whose disclosure is incorporated herein by reference, describes a method for collecting and processing physical space data for use while performing image-guided surgery. Physical space data is stated to be collected by probing physical surface points of surgically exposed tissue. The physical space data provides 3D coordinates for each of the physical surface points. Based on the physical space data collected, point-based registrations used to indicate surgical position in both image space and physical space are determined.
U.S. Pat. No. 9,019,262 to Ma, et al., whose disclosure is incorporated herein by reference, describes a method for transforming a displayed three-dimensional image corresponding to a position and orientation of a field of view of an imaging probe. A three dimensional image of a tissue in a first co-ordinate space can be displayed. A field of view of the imaging probe in a second co-ordinate space can be configured, and the first and second co-ordinate spaces can be co-registered.
US Patent application 2009/0299174, to Nelson, et al., whose disclosure is incorporated herein by reference, describes a method for tracking an instrument in a human patient. The instrument has an elongated body, such as an elongated flexible member, having a distal section configured to be passed through a vessel or other passageway in a human. The instrument can further include a lumen through the distal section and a magnetic marker having a transponder at the distal section.
Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that, to the extent that any terms are defined in these incorporated documents in a manner that conflicts with definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.